1. Field of the Invention
The present invention relates to a focus detection apparatus and a control method therefor, and an image capture apparatus using the same, which can be used for an automatic focus detection function.
2. Description of the Related Art
As a focus detection apparatus for detecting a focus state of an imaging optical system, Japanese Patent Laid-Open No. 58-24105 discloses an apparatus that performs focus detection of a so-called pupil-dividing type (also referred to as a phase-difference detection type) using a two-dimensional image sensor in which a microlens is formed in each pixel. According to the focus detection apparatus disclosed in Japanese Patent Laid-Open No. 58-24105, photoelectric conversion area of each pixel included in the image sensor is divided into a plurality of areas, and the divided photoelectric conversion areas receive light beams that pass through mutually different areas in a pupil of an imaging optical system via a microlens.
Furthermore, Japanese Patent Laid-Open No. 2005-106994 discloses an image capture apparatus that performs focus detection of a pupil-dividing type using a CMOS image sensor. According to the image capture apparatus disclosed in Japanese Patent Laid-Open No. 2005-106994, pixels (focus detection pixels) as part of the pixels included in the CMOS image sensor each have two divided photoelectric conversion areas, and are used to detect a focus state of an imaging optical system. Two photoelectric conversion areas included in one focus detection pixel receive light beams that pass through mutually different areas in an exit pupil of the imaging optical system via a microlens.
Furthermore, according to Japanese Patent Laid-Open No. 2013-72906, in the case of performing focus detection of a pupil-dividing type using an image sensor in which a photoelectric conversion area of each pixel is divided into two areas, an image shift amount is obtained from a result of obtaining a correlation data set for one pixel line and adding such correlation data sets of a plurality of successive pixel lines, so that the time necessary for focus detection calculation is shortened.
Performing such focus detection of a pupil-dividing type (imaging plane phase difference AF) using output signals of an image sensor for capturing images is advantageous in that focus detection can be performed at high speed in live view image capture and in that a sensor for focus detection does not have to be additionally provided. Meanwhile, in the configuration in which each pixel has two photoelectric conversion areas, it is necessary to determine as appropriate the amount of pixel data used for focus detection.
For example, if all pixels hold two pixel data sets in order to realize focus detection at any position in the screen, the buffer amount for holding pixel data is twice the conventional amount. Furthermore, if the amount of data held increases, the processing load for pixel data also increases. However, an increase in the processing time causes deterioration in the quality of user experiences such as deterioration in response of the apparatus, and, thus, high-speed processing has to be realized by a method such as performing parallel processing or increasing the operation clock. All configurations for increasing the buffer amount and realizing high-speed processing are costly, and, furthermore, if additional countermeasures against heat are required due to an increase in the amount of heat generated by the high-speed processing, the cost further increases.